Initialize DeferredTaskHandler's audio thread ID once.

third_party/WebKit/Source/modules/webaudio/DeferredTaskHandler.cpp

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 261 matching lines @@
 }
 
 void DeferredTaskHandler::clearHandlersToBeDeleted()
 {
     ASSERT(isMainThread());
     AutoLocker locker(*this);
     m_renderingOrphanHandlers.clear();
     m_deletableOrphanHandlers.clear();
 }
 
+void DeferredTaskHandler::setAudioThreadToCurrentThread()
+{
+    ASSERT(!isMainThread());
+    if (m_audioThread) {
+        ASSERT(m_audioThread == currentThread());
+        return;
+    }
+    ThreadIdentifier thread = currentThread();
+    releaseStore(&m_audioThread, thread);
+}
+
 } // namespace blink